This invention relates to a method for growing semi-insulating III-V compound semiconductor crystals by means of an epitaxially crystallizing process in the liquid state.
Generally, the liquid phase method for growing a crystal of a III-V compound semiconductor provides a higher quality crystal in a convenient manner in a relatively simple apparatus as compared with the gas phase method, and according to the former method, it is relatively easy to control the carrier concentration regardless of conduction type. For this reason, heretofore, the liquid phase method has been used to epitaxially grow crystals for Gunn diodes, IMPATT diodes, Schottky diodes, light emitting diodes, and laser diode semiconductors. However, according to the conventional liquid phase growing method, it has been impossible to obtain a crystal of a semi-insulating III-V compound semiconductor.
On the other hand, it is known from Japenese Pat. Publication No. 14,964/67 that a semi-insulating crystal having a resistivity of 10.sup.6 - 10.sup.8 ohm-cm can be obtained by the addition of chromium in growing a crystal of a III-V compound semiconductor by means of the Bridgman Method and the liquid encapsulation method. Nowadays, a semi-insulating bulk crystal is produced on an industrial scale by the addition of chromium.
In connection with the development of planarizing and integrating techniques, an epitaxially growing method has widely been used, and the liquid phase growing of chromium-doped semi-insulative III-V compound semiconductors has been tried. However, according to the conventional liquid phase growing method with the addition of chromium, it was impossible to obtain an epitaxial crystal of a semi-insulating III-V compound semiconductor having a high resistivity. Only a crystal having a low resistivity could be obtained (see "Material Research Bulletin" Vol, 4, pp. 149 - 152, 1969).
We have found as a result of the study for the liquid phase growing of chromium-doped semi-insulating III-V compound semiconductors that a semi-insulating III-V compound semiconductor having a desired resistivity can be obtained by reducing the concentration of residual free electrons and choosing an appropriate growing temperature.